Academic News
In 2024, a major multinational corporation achieved an optical efficiency of approximately 3% (1,300 nit/lm) with SRG-based lightguide technology at a 30° field of view, marking the highest publicly available efficiency data. However, when SRG is used as an external coupler, it can cause visible light emission from the wearer’s eyes and pose a security risk by reflecting displayed images outward.
A cross-institutional team led by Professor Ching-Cherng Sun of National Central University has achieved a 9% optical efficiency in volume holographic lightguide AR glasses, marking an improvement of over 500% compared to traditional volume holographic lightguide AR glasses. This also represents a 300% enhancement over the best data recorded internationally in 2024 using SRG technology.
The core goal of near-eye displays for augmented reality (AR) and mixed reality (MR) is to seamlessly integrate virtual images into the user’s environment while maintaining the transparency of the real world to enhance the immersive experience. To balance comfort, energy efficiency, and information security, the exit pupil expansion (EPE) of lightguide technology becomes critical. EPE enables a wide field of view and addresses challenges related to volume, weight, and user comfort. However, conventional EPE technology has relatively low optical efficiency, which affects market adoption.
In 2024, a major multinational corporation used SRG waveguide technology to achieve an efficiency of up to 1,300 nit/lm (~3%) at a 30° field of view, which is currently the highest publicly available optical efficiency data. However, when SRG is used as an out-coupler, it not only causes eye glow but also poses a risk of leaking the viewed image by reflecting it outward from the glasses.
In existing technologies, volume holographic optical element (VHOE) waveguides offer the best suppression of eye glow, the ability to expand the field of view through multiplexing techniques, an image quality of at least 33 PPD, and excellent color performance, making VHOE one of the top choices for EPE lightguides. However, the transmission wavelength of VHOE varies with the input angle, leading to energy loss and affecting optical efficiency.
Professor Ching-Cherng Sun stated that the cross-institutional AR/MR glasses research team, led by National Central University, has developed world-class diffractive lightguide technology. Their internationally leading advancements will be gradually published, with this research on lightguide efficiency being a significant achievement. The results have already been published in the top optics/photonics journal Laser & Photonics Reviews.
Professor Yeh-Wei Yu, a chief scientist of the research team, successfully derived an analytical solution for the wavelength distribution of EPE lightguides applicable to VHOE using the phase superposition theoretical model developed by Professor Sun, with experimental validation. By utilizing input images with characteristic wavelength distributions, the team ensured that image transmission at each angle achieved significantly high optical efficiency. Ultimately, they achieved a 9% optical efficiency at a 30° field of view—an improvement of 500% compared to traditional methods and 300% higher than the best-recorded SRG lightguide data.
Professor Yu emphasized that this technological breakthrough not only significantly enhances the optical efficiency of AR/MR glasses but also effectively reduces battery consumption, extending device battery life. This lays a solid foundation for the practical adoption and widespread use of AR/MR devices. With these advancements, the vision of AR/MR glasses as everyday portable devices is no longer an unattainable dream.
